Electrolytic apparatus



Jan. 16, 1923.

A. K. SMITH.

ELECTROLYTIC APPARATUS.

FILED JULY 29.192.

'IIIII II'IIIIII/II,

Base Meta! Nickd-ke. M2101 5 Adhereni Coafinq Containing The Oxide 01'Hydrox'ndn of Nickd or Cobdt.

INVENTOR.

ATTORNEY.

Patented Jan. 16, 1923.

. UNITED STATES PATENT OFFICE.

ALBERT KELVIN SMITH, or CLEVELAND, OHIO.

ELECTROLYTIC APPARATUS.

Application filed July 29, 1922. Serial No..578,498.

To all whom it may concern:

Be it known that I, ALBERT KELvIN SMITH, a citizen of the United States,residing at Cleveland, in the county of Cuyahoga and State of Ohio, haveinvented a certain new and useful Improvement in Electro- 1s gaseous,there is a phenomenon known as over-voltage, cons1st1ng of the excess involtage required to produce the actual evolution of the gases over thatwhich is theoretically necessitated by thermodynamic require ments. Atany voltage above the theoretical decomposition value there will'beproduced a collection of decomposition products at the surfaces of theelectrodes, but owing to this over-voltage condition there will be nomaterial evolution of the same in gaseous form until the impressedvoltagerises to a definitely higher amount which depends upon the natureof the solution, the concentration of the solution, the nature of theelectrodes, the surface condition of the electrodes, the temperature ofthe solution, and the current density. The consequences of thisover-voltage are a waste of power, which 15 the most expensive singleitem in the operation of most electrolytic processes, and the productionof local heat which it is sometimes inconvenient to dissipate.

Thus in the electrolytic production of oxygen and hydrogen, whatever bethe nature of the electrolyte, the hydrogen is evolved at the cathodeandtbe oxygen at the anode tial be employed. Ordinarily the best resultsare obtained with an electrolyte of potassium hydroxide for the reasonsthat its corrosive effect upon the electrodes is less than that of acidsand the solution offers a minimum of electric resistance. Such anelectrolyte enables the employment of nickel- (or'nickel-like)electrodes but these have the disadvantage of a high over-voltage,which, with customary current densities and electrolyte concentrations,ordinarily necessitate a potential of from 2% to 2% volts, whereas thetheoretical decomposition potential is only about 1% volts. This isequivalent to a power loss of from 45 to 50 per cent, which is not onlya serious item in it- Self but which tends to cause boiling and steamingand requires dissipation by cooling water. Likewise in the case of analkalichlorine cell wherein hydrogen is evolved at the cathode, the samephenomenon ofovervoltage appears at this point; and similarly in everyprocess wherein a part of the reaction consists of the decomposition ofwater 'or the evolution of one or both ofthe gases of which wateriscomposed.

It is well known that the electrode material which offers the leastover-voltage with respect to hydrogen is a plate of ,platinum coveredwith platinum-black, but this is prohibitively expensive'Ifor commercialuse. It has also been discovered that a coating of platinum-black whenapplied to the surface of some less noble metal such as nickel willserve nearly as well, and that nickel-black can be used in place ofplatinum-black with a very great advantage over the naked nickelelectrode (I refer to the application of Albert W. Smith filed November8, 1920, Serial No. 422,638). I have discovered, however, that there arecertain non-metallic, electrically-conducting, substances which can beemployed as a coating upon the electrodes with a very great decrease inthe over-voltage both of the oxygen and hydro gen; that these substancescan be formed in situ on the surfaces of the electrodes with a minimumof labor and expense; that they are highly satisfactory as regardspermanency either in the operating or in the waiting condition of theapparatus; and that their electrolytic performance equally rivals thatof platinized platinum.

My improved electrodes are characterized by the possession of anadherent coating providing that a current of suflicient potenconsistingof or containing the oxide or hydroxide-of nickel or cobalt, which caneither be pure or mixed with other substances such as finely dividedmetallic nickel or cobalt.

It is necessary that this coating be closely and firmly adherent and inorder to secure this condition I preferably form the same in situ. Oneof the best methods I have so far discovered of producing this coatingis as follows: The electrode is immersed in an ammoniacal solution ofnickel-nitrate made for example by dissolving 7 5 parts of nickelnitratecrystals in 1500 parts of water and adding 400 parts concentratedammoniumhydroxide solution (sp. g. 0.90). This electrode is now made acathode for a short period, say one to ten minutes, at room temperature,with a current density of from .nickel seems to vary with theconcentration, temperature, and current density. The current is nowreversed for about l;th the effective time of the first deposit; that isto say if the voltage is maintained constant I find that a period of %thaffords the best result, although at a lower potential the reversal cancontinue for a longer period. This causes the coating to become denserand more adherent and incidentally darker in color. The only reason forlimiting the time of reversal is that if maintained toolong the firstdeposition will be finally redissolved.

The current is now reversed again so as to make the electrode underformation a cathode, whereupon a second oxide layer is deposited uponthe first layer and this in turn is hardened and compacted by asucceeding reversal. This process is repeated until a deposit of thedesired thickness is obtained. I find that about four repetitions of theprocess produces a very satisfactory coatmg.

The electrode is now ready for use and can be employed in the usualmanner in all cases wherein the decomposition of water or the evolutionof either of the waterforming gases is effected with an alkalineelectrolyte; as in the production of oxygen and hydrogen for commercialpurposes, the cathode compartment of alkali-chlorine cells, and similarsituations. It can either be used immediately or stored and shippedwithout deterioration. Not only is this coating firmly adherent, but itis electrically conducting, sufficiently porous to afford a largeworking surface, and exhibits such a catalytic character as greatly toreduce the over-voltage either for hydrogen ,when used as a cathode orfor oxygen when used as an anode. When employed in an alkalineelectrolyte it appears to be proof even against the anode reaction, butit cannot be used in acid media.

It would appear that the beneficial operation of my improved electrodefor the purpose stated is due primarily to the presence of variousoxides of nickel (or nickellik metal), but the exact nature andcomposition of this coating is not important and perhaps notascertainable. It contains less oxygen than Ni 0 and more oxygen thanNiO, although the resenceof at least some proportion of Ni 3 can bedemonstrated. It is also impossible to determine with accuracy whetherthese oxides are present in the hydrated or dehydrated form, and thisindeed may vary to some extent depending upon whet-her the electrode isdried between formation and use. This point appears to have no practicalimportance to the operation of the apparatus, although it is believedthat ordinarily at least a part of the active substance is in hydratedform. Likewise the presence or absence of metallic nickel inthe coatingappears to be immaterial inasmuch as its proportion is generally verysmall and its inclusion in the larger volume of oxide blankets anyeffect it might otherwise exhibit.

In the drawing accompanying and forming a part of this application Ihave shown in unconventionalized form a pair of electrodes embodying myimprovements, those shown in Fig. 1 being of base metal plated withnickel-like metal, and those shown in Fig. 2 beingof homogenizedinternal structure. In either case they are provided with a smoothsuperficial coating containing an admixture of finely divided metallicnickel as shown in the above description. It will be understood thatthese electrodes may be made of any desired shape and size required b vthe design of the apparatus, and employed in any desired number; alsothat one electrode containing my improvements can be used in companywith an electrode of any other material or formation dependent upon thework in view.

By the employment of my improved electrodes for anode purposes in acaustic potash solution as employed in commercial oxygen production Ihave been able to reduce the over-voltage by about 0.2 volt from thatexhibited by the usual nickel electrode, and by its employment forcathode purposes in a similar solution as employed for oxygen productionI have been able to produce approximately the same economy. This amountsto a total power saving of approximately 20 per-cent when employed forboth terminals. Cobalt exhibits much the same effe ct as nickel althoughthe saving is slighter. Owing to the well known relationship between thenickel and cobalt I have included the two substances in my claims underthe expression nickel-like. Also by the word oxide or oxides I mean todesignate the hydrated oxide com ounds equally with the anhydrous forms0? the same. It will be noted that I have not specified the metal ofwhich the electrodes are made. Preferably I make the same superficiallyof nickel which may take the form either of a cast or rolled nickelplate, although the same may be made of some baser metal like iron orcopper plated therewith. However Ido not restrict myself to thisinasmuch as my improved coating can be plated directly upon some basermetal, nor do I limit myself in any other way except as specificallyrecited in the claims hereto annexed.

Having thus described my invention what I claim is:

1. Apparatus for the purpose described comprising,.in combination, apair of electrodes consisting at least superficially of nickel-likemetals having their faces covered with a porous, adherent, conductivecoating consisting essentially of a mixture of nickel- ]ike oxides.

2. Apparatus for the purpose described comprising an electrode ofnickel-like metal covered with a porous, adherent, conductive coatingcontaining a mixture of nickel-like oxides.

3. An electrode for reducing the over-voltage of the decompositionproducts of water characterized by having a superficial coveringcontaining the oxides of a nickel-like metal.

4. An electrode for the purpose stated having an adherent coating ofoxides of nickel.

5. The herein described process of forming an electrode which containsthe steps of subjecting a metallic plate to electrolysis in anaminoniacal nickel nitrate solution and slowly alternating the directionof current flow, while maintaining cathode conditions at said electrodeduring a larger proportion of the time than anode conditions.

6. An electrode for the low-voltage evolution of water-forming gasesfrom alkaline electrolytes consisting of an electrically conductingsupport coated with a porous, adherent, catalytic layer containingtheoxides of nickel-like metals.

In testimony whereof, I hereunto aflix my signature.

ALBERT KELVIN SMITH.

